Synthesis, Microbial Growth and Oxidation Inhibitory Properties of Three Mannich Bases

Abstract

Diseases, infections and unhealthy diet serve as threat to human existence. Bases obtained from Mannich reaction have been found to have pharmacological application as antioxidant, antimicrobial, anti-cancer, anti-hypertensive, antiviral and anti-inflammatory in drugs and as food additives. Biologically active 4-(3-oxo-1,3-diphenyl propylamino) benzoic acid (A1), N-phenyl-3-(phenylamino) propanamide (A2) and 3-(p-tolylamino)-N-phenylpropanamide (A3) were synthesized and their purity confirmed by melting point determination and Thin layer chromatography. Characterization of the Mannich bases by spectroscopic methods: Infrared and Ultraviolet spectroscopy confirmed the presence of C=O, O-H, N-H typical of Mannich bases. They are also readily soluble in organic solvents. Antioxidant activity of A1, A2 and A3 involving the use of 2,2- diphenyl-1-picrylhydrazyl radical (DPPH) and hydrogen peroxide was significant when compared with antioxidant standards: ascorbic acid, butylatedhydroxylanisole and α-tocopherol. Compounds A2 and A3 gave percentage inhibition of 90.37 and 90.11 at 0.0625 mg/ml in the hydroxyl radical scavenging activity, a better percentage inhibition than ascorbic acid and α–tocopherol at the same concentration. Antimicrobial activity of the three compounds against bacterial and fungal strains; Staphylococcus aureus, Escherichia coli, Bacillus subtilis, Pseudomona aeruginosa, Klebsiellae pneumoniae, Salmonellae typhi, Candida albicans, Aspergillus niger, Rhizopus stolonifer and Penicillium notatum showed moderate microbial inhibition when activity was compared with standard drugs: gentamicin and tioconazole for bacteria and fungi respectively. The ionization constant (pKa) values at 6.01, 8.15 and 7.23 reported for compounds A1, A2 and A3 respectively indicates that they would be readily metabolized at physiological pH.

Keywords: Mannich bases; spectroscopy; oxidation; antimicrobial; ionization constant